The molding of lignocellulosic and lignocellulosic containing fibers, particles or layers to form composite articles is known. The binders which normally are used are the synthetic resin glues such as a solution of ureaformaldehyde or phenol-formaldehyde resin in water. Composite products containing lignocellulose produced in this way lack durability and are susceptible to moisture conditions and deterioration in certain building purposes to which they may be subjected.
Di- and polyisocyanates as binders for lignocellulose materials have been proposed and are known to give products of increased stability and mechanical strength. Process technical advantages of polyisocyanates have been disclosed in German Offenlegungsschrift No. 2,109,686. One problem associated with the use of polyisocyanate binders is that the viscosity of the normally employed polyisocyanate binders are much higher than the synthetic glue resins and are therefore difficult to apply to the lignocellulose with current application equipment or methods. The advent of technology to emulsify the polyisocyanates in water provided a binder product with reduced viscosity but with a service life of only 2 to 4 hours.
The present invention which comprises an improved polyisocyanate based adhesive binder composition that has been extended through the addition of a liquid aromatic epoxide having one .alpha. epoxide group and/or aromatic or aliphatic based multifunctional epoxide having 2 or more epoxide groups, and lignin, avoids the above mentioned disadvantages.